RADON MITIGATION SYSTEM SERVICE CALL

If your radon system needs an evaluation, repair, or a thorough checkup, we have the solution.

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This comprehensive diagnostic +50 point checklist is designed to troubleshoot active sub-slab depressurization (ASD) systems and identify radon entry pathways. We also offer specialized checklists for other system types and unique mitigation challenges.

 

1. Active Mitigation Fan & System Diagnostics

• U-tube manometer reading: Verify liquid levels are offset and record the pressure reading in inches of water column (WC).

• Fan power status: Ensure the fan is receiving electrical power and running continuously without interruption.

• Fan housing condition: Inspect the exterior fan housing for cracks, UV degradation, or water damage.

• Fan vibration & noise: Check for excessive vibration, humming, or grinding noises indicating bearing failure.

• Fan sizing evaluation: Verify the fan model matches the current pressure and airflow needs of the soil.

• Electrical disconnect switch: Confirm a dedicated, weatherproof electrical disconnect switch is installed near exterior fans.

• Condensate bypass installation: Ensure the fan setup allows condensed water to drain past the fan impeller safely.

• Exhaust piping pitch: Check that all horizontal vent piping slopes back toward the suction pit to drain water.

• Exhaust stack height: Verify the vent discharge terminates at least 10 feet above ground level.

• Exhaust stack clearance: Confirm the exhaust is 10 feet away and 2 feet above any window, door, or opening.

• Exhaust termination cap: Check that the pipe end has a protective screen to block debris and pests without a restrictive cap.

• System labeling: Verify the vent pipe features prominent, clear labels marking it as a radon mitigation system.

 

2. Suction Pit & Sub-Slab Communication

• Suction pit depth: Check the depth and volume of the dug-out pit underneath the slab penetration.

• Aggregate check: Evaluate if the material under the slab is loose gravel, tight sand, or dense clay.

• PFE testing (Pressure Field Extension): Drill small test holes at distant slab points to measure sub-slab vacuum.

• Micromanometer verification: Use a digital micromanometer to confirm at least -0.025 water column inches at test holes.

• Suction pipe seal: Inspect the polyurethane sealant joint where the PVC pipe penetrates the concrete slab.

• Slab thickness assessment: Measure concrete slab thickness through test holes to evaluate structural resistance.

• Multiple suction points: Determine if interior footings require adding secondary suction points to bridge separated slab areas.

 

3. Concrete Slab & Foundation Wall Integrity

• Slab crack inspection: Map and check all visible floor cracks for active soil air leaks using a smoke pencil.

• Expansion joint sealing: Inspect the perimeter expansion joints where the slab meets the foundation walls for gaps.

• Control joint evaluation: Check all saw-cut control joints to ensure they are completely sealed with elastomeric sealant.

• Crawl space vapor barrier: Inspect membrane thickness (minimum 6-mil, preferably 30-mil) and verify it covers 100% of the soil.

• Vapor barrier seam tape: Confirm all crawl space membrane seams are overlapped 12 inches and taped securely.

• Vapor barrier wall attachment: Ensure the crawl space membrane is sealed to the foundation walls with polyurethane caulk or furring strips.

• Block wall top-caps: Inspect the top course of concrete block walls to see if they are open or sealed shut.

• Wall-to-floor joint leakage: Check for air bypass at the cove joint using chemical smoke or a thermal camera.

• Utility penetration seals: Inspect gaps around sewer lines, water mains, gas lines, and electrical conduits.

 

4. Drainage Systems & Sump Pump Basins

• Sump pit cover seal: Check that the sump basin has an airtight, gas-permeable gasketed lid.

• Sump lid view port: Ensure the sump cover features a clear, sealed window to inspect pump operation.

• Sump discharge pipe seal: Verify the rubber grommets or caulking around the pump discharge pipe are airtight.

• Sump power cord grommet: Check the seal around the electrical power cords exiting the sump basin.

• Sump pump check valve: Verify the check valve prevents backflow and does not cause excessive physical system vibration.

• Floor drain traps: Confirm all floor drains have active water traps or mechanical trap-seal devices (like Dranjer valves).

• Perimeter French drain isolation: Check if interior perimeter drain tile systems are open to air or sealed off.

• Exterior drain tile termination: Inspect where outdoor foundation drains terminate to ensure radon is not pulling back through them.

 

5. Indoor Air Dynamics & HVAC Interaction

• Air handler pressure effects: Measure radon levels while the central heating and cooling fan is actively cycling.

• Return ductwork leakage: Inspect negative-pressure return ducts in unconditioned spaces (like crawl spaces) for leaks.

• Supply ductwork leakage: Check for positive-pressure supply duct leaks that could drive building depressurization.

• Combustion appliance backdrafting: Conduct a worst-case draft test on natural draft water heaters or furnaces.

• Exhaust fan depressurization: Measure the pressure drop caused by kitchen hoods, clothes dryers, and bathroom fans.

• ERV/HRV balance: Check the airflow balance of Energy Recovery Ventilators to avoid negative indoor pressure.

• Outdoor air intake positioning: Ensure HVAC fresh air intakes are located away from the radon vent exhaust stack.

• Whole-house fan evaluation: Evaluate the depressurization risk when large ceiling-mounted exhaust fans are running.

 

6. Environmental Conditions & QA Testing

• Barometric pressure trends: Track local weather patterns and barometric pressure drops during diagnostic testing phases. This is best done with long term continuous radon monitoring.

• Soil moisture saturation: Assess whether rain or high water tables are blocking sub-slab air communication pathways.

• Wind load effect: Check if high winds are altering building pressure fields or creating a stack effect.

• Short-term charcoal tracking: Deploy 48-hour charcoal canisters to verify rapid system drawdown efficiency.

• Continuous Radon Monitor (CRM): Run a calibrated CRM to monitor hourly spikes and verify overall system stability.

• Multiple simultaneously radon tests, performed in different rooms and different levels of the home at the same time if possible, will often yield the most helpful test data.

 

To troubleshoot a specific radon system that is not performing as it should, we will need to determine critical building and radon system information such as:

• A copy of all past radon tests performed at the property.

• What is the current radon reading and manometer level?

• What type of foundation does the house have (basement, slab-on-grade, crawl space)?

• Are you dealing with a new installation or fixing an existing system failure?